1. Field of the Invention
The present invention relates to an organic surface-treating agent and more specifically to an organic surface-treating agent which is useful as a surface-treating and dispersing agent for an inorganic material, in particular, an inorganic powder, to increase its dispersibility in a solvent.
2. Description of the Related Art
In general, since the surface of an inorganic material or powder is hydrophilic, its wettability and dispersibility with an organic solvent or a polymeric binder is poor. Therefore, in the production of paints, it has been the practice to modify the surface of the inorganic material or inorganic powder with a silane coupling agent (see Elements of Chemistry (Kagaku Sosetsu) No 44, "Surface Modification" edited by Japan Chemical Society (published by Gakkai Shuppan Center)).
In addition, dispersibility of the inorganic powder is important, in particular, in the production of a magnetic paint, since the recording density of a magnetic recording medium which is produced using the magnetic paint directly relates to the dispersibility.
In the field of magnetic paint, based on the basic idea that the dispersibility of magnetic powder or a filler can be improved by the use of a dispersant which has a hydrophilic or reactive functional group on at least one end of a lipophilic backbone of a molecule, the surface of such a powder is modified with a fatty acid or various surfactants as a surface-treating agent (cf. Japanese Patent Kokai Publication No. 102504/1983), or a silane coupling agent or a titanium coupling agent (cf. Japanese Patent Kokai Publication Nos. 125539/1980 and 58135/1981).
As suitable organic solvents in which an organic material is dissolved, toluene, MEK, ethyl acetate, THF and the like are known. Ethyl acetate contains an ester group, THF contains an ether group, MEK contains a ketone group, and toluene contains a phenyl group.
Since the conventional fatty acid or silane coupling agent does not contain the ester, ether or phenyl group in its backbone, it has poor compatibility with these organic solvents.
In addition, since such a fatty acid or silane coupling agent has a very small average molecular weight, it cannot increase the distance between particles of the organic powder. Therefore, the once dispersed organic powder particles recoagulate.
Such a fatty acid or silane coupling agent is insufficient for dispersing the organic powder stably in the presence of the organic solvent.
It has been tried to increase the dispersing capability of the polymeric binder for the inorganic powder by incorporating a hydrophilic or reactive functional group such as a sulfonic acid group, a phosphoric acid group, a carboxylic acid group or their salts, or a tertiary amino group in the molecular chain of the binder (Japanese Patent Kokai Publication Nos. 13520/1981, 117734/1980 and 13223/1989). However, such polymeric binders do not have sufficient dispersing capability, and it is necessary to provide a new surface treating technique in order to increase dispersibility.